A solar eclipse is when the moon passes between the Earth and the Sun and the moon fully or partially blocks the Sun.

In a fortunate twist of fate, the Sun is 400 times larger than the Moon but it is also 400 times further away. This means, when you line them up, they are almost the same apparent size in the sky. This means when the smaller, closer Moon aligns with the larger, more distant Sun, they can completely cover each other if they are correctly aligned. This is a funny skit from an Irish TV show called Father Ted that explains the idea :D http://www.youtube.com/watch?v=vh5kZ4uIUC0

Because the Moon's orbit around the Earth is not completely circular, and because the Earth's orbit around the sun is not completely circular, the apparent size of the moon and the Sun vary. The Sun appears largest when the Earth is near it, in January. When the moon is farthest from the Earth, or the Sun is closest to the Earth, the moon won't quite completely cover the Sun. In that case the eclipse is called "annular", because a ring or "annulus" of the Sun is uncovered. That's what we had this past May. Trigger posted a movie of this year's annular eclipse on his facebook page https://www.facebook.com/Trigger.MMS and on our Youtube channel http://www.youtube.com/embed/P-L0BSYsgfo I'll be going to the eclipse in Australia next month... look for Trigger's pictures on his facebook page!